error of bash string concatenation

Question

For me bash script is always some kind of tricky. I have

web_dir=/tng4/users/ldiao/AQF/wrf-chem-result/
rm "$web_dir""three_days_ago/*.gif"

the error message is

rm: cannot remove '/tng4/users/ldiao/AQF/wrf-chem-result/three_days_ago/*.gif': 
No such file or directory

But if I change to

rm "$web_dir"three_days_ago/*.gif""

then it works. There is no spell errors. Can someone explains for me the reason? thanks!

The globbing characters *, ? etc are not expanded within quotes, but they are interpreted literally. To find out why they designed it like this, you would probably have to ask one of the language's developers. — user000001
– user000001, Commented Aug 21, 2013 at 16:51

Aleks-Daniel Jakimenko-A. · Accepted Answer · 2014-07-06 01:27:01Z

6

The reason is that bash globbing does not work inside " "

Correct variant would be

rm -- "$web_dir/three_days_ago/"*.gif

Also, use -i option when playing with rm. This way if you make a mistake or a typo it wont delete all of your files unless you confirm that.

edited Jul 6, 2014 at 1:27

answered Aug 21, 2013 at 16:52

Aleks-Daniel Jakimenko-A.

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3 Comments

tripleee Over a year ago

And just to be precise, your second example works because you have $web_dir properly in double quotes, followed by unquoted three_days_ago/*.gif, followed by a completely superfluous double-quoted empty string. For what it's worth, the idiomatic way to quote that would be something like "${web_dir}three_days_ago"/*.gif

Aleks-Daniel Jakimenko-A. Over a year ago

@tripleee I always suggest to use extra / between variables. Just in case you forget to end your variable with a slash. Two slashes wont hurt. So I'd edit your example to "${web_dir}/three_days_ago"/*.gif. Also it seems like there's no difference if you put a slash after the quote or right before it.

tripleee Over a year ago

Right, the slash is not a metacharacter to the shell, so it doesn't require quoting; but on the other hand, quoting regular characters is harmless.

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